The prior art is replete with lubricant formulations useful in the hot rolling of metals such as aluminum.
With the evolution of hot rolling equipment toward rolling mills that produce higher pressures at ever-increasing operating speeds, the demands placed on the lubricants used in such mills have increased with each new generation of rolling equipment. Such increasing demands have resulted in further expansion of the list of lubricant formulations useful in hot rolling operations.
To the best of our knowledge, however, all of the "new and improved" formulations possess certain inherent problems, some or all of which to date have not been solved by any one formulation. For example, Knepp U.S. Pat. No. 4,243,537 requires the use of fatty acids, which are known to be depleted during use through their conversion to metallic soaps, eventually resulting in unstable and inadequate lubrication, as well as interfering with general lubricant manageability. An object of the present invention, not realized by Knepp, is the elimination of fatty acids and their precursors. The use of complex organic phosphate esters in compositions with and without fatty acids and their precursors is known in Sugiyama U.S. Pat. No. 3,945,930. However, Sugiyama does not recognize that the use of certain polyalkylene glycol polymers will synergistically enhance the lubricating performance of complex organic phosphate esters, further eliminating the need for harmful fatty acids and their precursors. Exploitation of this synergistic behavior is a further object of the present invention. In the lubricant compositions of the prior art, there are problems related to: (1) physical stability, (2) high temperature capability, (3) chemical stability, (4) inability to withstand extreme pressure lubrication conditions over extended periods of use, (5) corrositivity, and (6) tolerance of reclamation processes.
Each of these characteristics is familiar to the skilled lubricant technician. Physical stability relates to the ability of the lubricant components to remain as initially formulated without separating into macroscopically observable multiple phases. Such separation is characteristic of macroemulsions and is one means for distinguishing between macroemulsion and microemulsion lubricant types. Microemulsions also are visually translucent or transparent in appearance as a result of the dispersed phase droplets being predominately less than 0.2 micrometers in diameter. High temperature capability defines the ability of the lubricant to tolerate the temperatures required for and produced in metal-working operations without one or more of the components evaporating or undergoing chemical degradation to such an extent that the composition of the lubricant bulk would be altered. Additionally, high temperature capability includes the ability of the lubricant to extract heat from the metalworking operation at a rate and in a manner which is beneficial to the manufacturing equipment and to the end product. Chemical stability describes the capacity of the lubricant to not undergo chemical changes, in storage or in use, which would adversely affect the metalworking operation. The ability to provide adequate extreme pressure lubrication defines the ability of the lubricant to reduce or prevent conditions of seizure or welding between the tool, e.g., the rolling mill, etc., and the workpiece under conditions of extreme load. Corrositivity relates to adverse chemical attack on the metal-working machinery and/or the workpiece. The ability to tolerate reclamation processes relates to the lubricant's capacity to undergo, without physical or chemical degradation and/or significant depletion of the lubricant's ingredients, those physical and/or chemical operations which are designed to remove fines, dirt, and other contaminants of the metal-working operation. These reclamation processes further include reconstitution of any constituents of the lubricant which have undergone depletion or dilution during use of the lubricant.
Thus, it has been the aim of the formulators of lubricants to design a formulation which eliminates or alleviates all of the foregoing problems.